There is scarce information on the natural history of cataracts. Although cataracts are the most common cause of blindness in the world, and cataract surgery is the most commonly performed surgery of the eye, the etiology of cataract is unknown and little is known about its natural history. Cataracts grow very slowly, usually taking years, making it difficult to conduct longitudinal studies because of the long study times. We have tested and refined subjective and objective methods of documenting and monitoring cataracts. Reproducibility studies in our clinic showed excellent reproducibility of the LOCS II clinical and photograding systems, the Zeiss Scheimpflug/NEI Imaging System and the Oxford/NEI Imaging system. We conducted initial longitudinal studies which showed these systems can pick up significant changes in cataracts of various types within one year. Those patients with cataracts were more likely to progress than those without any cataract. We are presently continuing these longitudinal studies. We are also exploring new methods of documenting cataracts as they are developed, such as the Quasielastic laser scattering device and magnetic resonance imaging. The data we are collecting will be useful in determining progression rates of cataracts of various types and will also be useful in planning future anticataract drug trials.